The excavated muck holes are unmarked locations in the Fallout 3 add-on Point Lookout, found 1 block east and slightly north of the Lil' Tyke Playhouse. They are part of the An Antique Land side quest.
The excavated muck holes are the result of a Bysshe Company pre-War research team surveying bio-gas. The muck holes are heavily irradiated, abandoned, contain gas pockets, and contain the soil sample holotapes. **Warning** Be advised if you are partial to flame based weapons, merely stepping into a pocket of gas while equipped with the flamer, Shishkebab, or various other flame weapons, with it drawn, will cause the gas to ignite, setting you on fire. Likewise, drawing such a weapon while standing in gas will also cause it to ignite.
Sample site one
This excavated muck hole is north of the trash heap. Inside there is a desk with a few items on it, such as:
Outside the muck hole is a destroyed shack surrounded by a muck pool. A mini nuke can be found in an open safe next to the bed frame on top of the heap.
Sample site two
This excavated muck hole is 1 block east and slightly north of the Lil' Tyke Playhouse. Inside there is:
Outside the muck hole there is a desk, a couple feral ghouls and a muck pool.
Sample site three
This excavated muck hole is northwest of the jet crash site. Inside there is:
Outside muck hole 3 is a destroyed shack with a table and a ham radio.